A conventional anti-vibration apparatus employs arrangements as shown in FIGS. 18A to 18C. In the arrangements shown in FIGS. 18A to 18C, as an anti-vibration element, one which utilizes the displacement of an elastic spring 1760 (FIG. 18A: spring support), one which utilizes the repulsive forces of homopolar magnets 1770 (FIG. 18B: repulsive magnet support), and one which utilizes the damping effect of rubber seal cylinders 1790 (FIG. 18C: rubber seal cylinder support) are respectively inserted between a base 1720 where a semiconductor manufacturing apparatus such as an exposure apparatus is placed and a worktable 1710 where a driving element such as an X-Y stage and other precision components and precision apparatuses are placed. Vibration propagating from the base 1720 is absorbed by such an anti-vibration element, so that the worktable 1710, or the entire exposure apparatus, or the like, is vibration-controlled.
Also, vibration caused by the driving reaction force generated by a driving element such as the X-Y stage arranged on the worktable 1710 is absorbed by the anti-vibration element described above, so that dark vibration propagating to the base 1720 is removed.
An example of such an anti-vibration apparatus is disclosed in Japanese Patent Laid-Open No. 08-270725.
Different anti-vibrating schemes shown in FIG. 18A to 18C have the following problems.
The rubber seal cylinder 1790 (FIG. 18C) serves as an air spring, and is constituted by a column 1730, cylinder 1740, and rubber seal 1750. The cylinder 1740 is filled with air 1780. When the column 1730 displaces, the air 1780 is compressed, and the spring constant of the air 1780 changes in accordance with the compressed state of the air 1780. Hence, according to this scheme, a large load is supported in the support direction. Even when the large load is supported, it can be absorbed as a displacement without propagating the force. The spring constant in the support direction (z direction) is set to a low value as an initial value. When a large load is received, the air 1780 in the cylinder 1740 is compressed in accordance with the load, so that the spring constant of the air 1780 increases. The load and the displacement of the spring gradually stabilize and are supported because of the balance of the load and air 1780.
As the spring constants in directions (x and y directions) perpendicular to the support direction (z direction) are larger than that in the support direction, a vibrating force of the x-y plane is undesirably likely to be transmitted to the worktable.
Assuming a large load in the support direction (z direction), the spring constant of the elastic spring 1760 (FIG. 18A) represented by a coil spring is limited to a certain degree due to the relationship with respect to an allowable displacement. Hence, it is difficult to support a large load and to set a small spring constant simultaneously. If the two demands are forced to be met, the spring itself may become large in size, or surging due to the spring mass may occur to degrade the anti-vibration performance.
This applies in a case wherein the repulsive forces generated by the homopolar magnets 1770 are utilized. If the homopolar magnets are set to face each other as shown in FIG. 18B to generate repulsive forces, to support a large load and to design a small spring constant in the support direction (z direction) cannot be achieved simultaneously. The anti-vibration performance of absorbing a force (large load) in the support direction as a displacement is limited to a certain degree. Hence, the force (large load) is undesirably likely to be transmitted to the worktable 1710 as an applied vibration source.
In the support scheme where an elastic body (spring) or magnets are used, the spring constant of the anti-vibration element is set in advance by setting constant load conditions for the worktable. When, for example, the X-Y stage described above is driven and serves as a moving load to change the barycenter of the worktable 1710, or when a component or the like to be placed is replaced, so that the load conditions for the worktable itself change, the support force cannot be changed accordingly.